1. Technical Field
The present invention is related to an electrostatic switch for high frequency and a method for manufacturing the electrostatic switch for high frequency, more specifically to an electrostatic switch for high frequency and a method for manufacturing the electrostatic switch for high frequency that can be applied with the MEMS technology, can be simpler in the manufacturing process through improvement of the structure and can be made smaller.
2. Description of the Related Art
With the recent technological development of ultra-compact precision devices, electronic components, such as a switch, installed in these devices are increasingly required to be smaller, lighter and more high-functional. Accordingly, there has been an increased demand for application of the MEMS (Micro Electro Mechanical System) technology.
The electrostatic switch applied with the MEMS technology, which is an electrical switch substituted by a mechanical switch, has an improved insertion loss characteristic in a high frequency band and shows superb signal separation. Moreover, not only is the power loss reduced according to the switch driving method, but the linearity is improved and the distortion and interference of a signal can be reduced.
FIG. 1 is a sectional view of a conventional electrostatic switch for high frequency.
A conventional electrostatic switch for high frequency 10 includes a lower substrate 12, on which an insulating film 11 is formed, and an electrode part 14, which is formed above the lower substrate 12. A pair of CoPlanar Waveguides (CPWs) 16, which are for allowing an RF signal to pass, are formed on either side of the electrode part 14.
Formed above the electrode part 14 is a dielectric 15. Installed above the pair of CPWs 16 across an upper area of the electrode part 14 is a membrane 18, and a gap is provided between the electrode part 14 and the membrane 18 by the height of the CPWs 16.
The pair of CPWs 16 guide the RF signal to pass. Electric power applied when a signal is generated is supplied to the electrode part 14, and an electromagnetic field is formed around the electrode part 14. The electromagnetic force of the electromagnetic field around the electrode part 14 pulls the membrane 18, which is then bent and makes contact with the dielectric 15 of the electrode part 14.
A method for manufacturing the conventional electrostatic switch for high frequency 10 is as follows.
First, the electrode part 14 is installed above the lower substrate 12, and the dielectric 15 is installed above the electrode part 14.
Then, after the CPWs 16 are formed, a sacrificial layer is formed above the lower substrate 12 and the dielectric 15. Here, the sacrificial layer is formed with a thickness that is sufficient for the membrane 18 to bend easily.
Afterwards, an area of the sacrificial layer excluding the pair of CPWs 16 is removed between the membrane 18 and the electrode part 14.
FIG. 2 is a sectional view of a conventional electrostatic switch for high frequency in accordance with another embodiment.
Referring to FIG. 2, an electrostatic switch for high frequency 20 has an electrode part 24 formed above a lower substrate 22 and a dielectric 25 formed above the electrode part 24.
Formed on either side near the electrode part are CPWs 26, above which a membrane 28 is installed. The membrane 28 is separated from the electrode part 24 by a certain distance, for which arch-shaped anchors are formed over the CPWs 26 on either side of the membrane 28.
In this type of electrostatic switch for high frequency 24, an electromotive force can be generated by bias voltage inputted to the electrode part 24, and the membrane 28 can be deformed about the anchors and make contact with the electrode part 24.
In the conventional electrostatic switch for high frequency 10, 20, it is required to introduce a process of using/removing a sacrificial layer in order to form a gap between the membrane 18, 28 and the electrode part 14, 24. Here, used for the sacrificial layer can be polymer, such as polyimide or photoresist, or oxide/nitride film. However, materials that can be used for the sacrificial layer are limited depending on the preceding/following process, and use of the sacrificial layer is also limited depending on the materials used in the preceding/following process or the material used in the sacrificial layer.
In the electrostatic switch for high frequency 10 having a pair of CPWs 16, the membrane 18 needs to be maintained flat in order to provide the structural stability. However, some etching can occur on an upper portion of the CPWs 16 during the removal of the sacrificial layer, and accordingly it becomes difficult to form the upper portion of the CPWs 16 flat. As such, the manufacturing process of the electrostatic switch for high frequency 10 having the CPWs 16 does not allow for a perfectly flat structure and thus encompasses an inherent structural weakness.
Moreover, in the electrostatic switch for high frequency 20 in which the membrane 28 is supported by the anchors, the deformation of the membrane 28 can cause fatigue in the structure to be accumulated with an extended use and can result in damage.
In addition, an additional process of protecting a chip by capping an upper portion of the membrane 18, 28 has been conventionally required in order to protect the structure and maintain the characteristics after the electrostatic switch for high frequency 10, 20 is made. This, however, makes the manufacturing process more complex, increasing the manufacturing cost and lowering the production yield.
Furthermore, since a connection electrode for mounting the electrostatic switch for high frequency 10, 20 needs to be formed after the conventional the electrostatic switch for high frequency 10, 20 is packaged, the overall size of the product becomes is increased and an additional process for forming the connection electrode is required.